Process for impact extrusion of aluminum alloys

ABSTRACT

A PROCESS FOR THE INVERSE WIRE DRAWING BY SHOCK OF ALUMINUM ALLOYS WITHOUT THE ADHERENCE OF PARTICLES OF METAL ON THE STAMPED MEMBER BY PRECOATING THE SURFACES OF THE BLOOM COMING IN CONTACT WITH THE STAMPED MEMBER WITH ZINC WHEREBY THE OPERATION CAN BE CARRIED OUT SUBSTANTIALLY CONTINUOUSLY WITHOUT THE FORMATIONS OF STRIATIONS, CRACKS OR GOUGES IN THE SURFACES CONTACTED BY THE STAMP.

United States Patent,

3,608,345 PROCESS FOR IMPACT EXTRUSION 0F ALUMINUM ALLOYS Henri Bouchereau, Clermont-Ferrand, and Marc Anagnostidis, Chamalieres, France, assignors to Societe Metallurgique de Gerzat, Paris, France No Drawing. Filed Nov. 1, 1967, Ser. No. 679,627 Claims priority, applicatgosn 0France, Nov. 15, 1966,

Int. Cl. B210 23/20, 23/24, 23/30, 23/32, 23/18 U.S. Cl. 72-47 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the processing of aluminum alloys by the inverse of wire drawing or by shock.

Wire drawing by shock or impact consists of forcing the metal, in the form of a rough bar or bloom, to flow under pressure into an annular space formed between a stamp punch and matrix. In wire drawing, the metal from the bloom is pulled directly by a draw bench through a die to lengthen the stamp in the direction of displacement. The metal flows in the inverse direction in inverse wire drawing by shock, which is sometimes referred to as backward extrusion.

Inverse wire drawing or backward extrusion, which is used with goods results with aluminum of commercial grade, runs into a number of serious problems when applied to alloys of aluminum and the difficult increases with the increase in the alloy content of the aluminum alloy. In such instances, it is often impossible to conduct more than two or three successive operations before inverse wire drawing becomes impractical from the standpoint of the operation and results.

Because of the tendency of metal particles to adhere to the stamp, the products that are formed have defects on their interior surfaces such as striations, gouging of metal and cracks, which render such products commercially unacceptable. It is therefore necessary frequently to clean the tools, either chemically or mechanically, thereby to make it impractical to carry out an economical continuous or sequential operation.

It is an object of this invention to provide a new, practical and efficient process for the inverse wire drawing by shock of aluminum alloys and it is a related object to provide a process of the type described which avoids the adherence of metal particles on the surface of the stamp used to effect inverse wire drawing by shock.

It has been found that the difficulties heretofore experienced can be overcome when the portions of the bloom surface engaged by the stamp are provided with a coating of zinc prior to the processing of the bloom by inverse wire drawing by shock.

Wire drawing of aluminum alloys by shock with a high speed mechanical or hydraulic press is of considerable interest to the trade 'because a number of advantages are capable of being derived with respect to the process as commercially practiced on alloys of the type described by hot drawing on a hydraulic press. Some of the advantages are listed as follows:

(1) Rapidity of excretion;

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(2) Economy of metal because of the precision of the finished part and the excellent surface finish obtained;

(3) Good orientation of fibers resulting from the elongation of the metal grain of the bloom;

(4) Grain fineness and regularity;

(5 High mechanical properties.

Inverse wire drawing is a very simple and rapid means for producing products having a base and cylindrical walls or of other geometrical shapes. On the other hand, such process cannot be practiced with aluminum alloys without the adherence of metal particles on various parts of the stamp with the result that the drawn products are formed with defects on their interior surfaces, such as striations, gouges or cracks.

By way of illustration, cylinders having a diameter of 46 mm. and a height of 52 mm. are drawn from blooms of aluminum alloy identified as AU6 MGT, reference being made to the French standards AFNOR No. A0200l and A02002. The blooms are not given any particular surface treatment except that they are lubricated with lanolin and zinc stearate and the head of the stamp is largely rounded off.

After ten such blooms have been drawn, particles of the alloy are found to adhere on the rounded part of the stamp head, on the one hand, and on the wire drawing arrest, that is, the largest part of the stamp situated a short distance above its base, on the other hand. Bands of sticking also arise at the center of the rounded surface, pass over the wire drawing arrest and end in the form of spearheads having their points aimed towards the top of the stamp. The interior surfaces of the drawn product have streaks of striations formed by the deposit of metal particles on the stamp. The position of the adhered bands, their shape and direction, shows that the metal on the stamp is secured during drawing and not during extraction, as evidenced by the streaks formed on the interior surfaces of the drawn products. We have sought to remedy the defects by coating the bloom with a metal capable of preventing the deposit of metal particles from the bloom onto the stamp during the processing steps.

Copper, used in the drawing of metals which are not malleable, such as beryllium, was one of the metals tried. With copper, with the very first piece, many streaks were obtained in the lower half of the drawn product while the upper half had some very wide shallow cracks.

After removal of the copper coating with acetic acid, the described defects became even more pronounced.

With tin, striations appeared after about ten drawings although the striations were not pronounced and were concentrated only in the lower fourth of the drawn product. On the other hand, noticeable defects were localized in the upper quarter in the form of large cracks having a depth as much as 1 mm. These became even more pronounced after removal of the tin coating.

On the other hand, zinc acted uniquely by comparison with other metal coatings. With zinc, full protection was secured of the stamp and the drawn products. No traces of striations were found after drawing one hundred blooms in which the surfaces of the blooms were precoated with zinc. The zinc became distributed easily over the upper half of the drawn products. After removal of zinc from the drawn products, as by solution in nitric acid, the surfaces still appeared smooth and without streaks, striations or cracks.

The coating of zinc can be effected on the surface of the bloom of the aluminum alloy by conventional means such as by chemical means, electroplating, immersion in a molten bath of the metal, by sputtering or by molten metal coating. Effective results are secured when the zinc coating is applied to the surfaces of the bloom coming in contact with the stamp in thicknesses which may range from 0.15 to 0.40 and preferably 0.2 to 0.25 mm.

The following example is given by way of illustration, but not by way of limitation. A tubular receptacle is produced by inverse wire drawing in which the receptacle has an external diameter of 74.2 mm., an interior diameter of 63 mm., a height of 212 mm., and a wall thickness in the bottom of 9 mm. The receptacle is fabricated of an aluminum alloy type AU4G from a bloom having a diameter of 74 mm. and a height of 70 mm.

Before the described inverse wire drawing to form the receptacle, the bloom is first annealed and then slowly cooled, in the case of a heat treatable alloy. One of the plane faces of the bloom is then ground with steel shot thrown at a sharp acute angle. The face so processed is provided with a coating of zinc having a thickness of 0.2 to 0.3 mm. in which application is made by sputtering. The coated bloom is then lubricated with a conventional lubricant such as lanolin and zinc stearate.

The inverse wire drawn receptacle is subjected to the conventional treatment of immersion in cold water, heating to 495 C. and maturing for 15 days at about 20 C. and the product gave the following measurements:

Elastic limit: 31 to 32.2 hectobars Breaking load: 49 to 50.1 hectobars Elongation: 23.5 to 24.5 percent Elongation is measured on the initial length equal to 5.65 times the square root of the section of the test piece.

The results secured are about 50 percent higher than the values normally obtained in producing the same product of the same alloy by present conventional means.

The process of this invention can be employed with a large number of aluminum alloys and particular benefit is derived with the practice of the process of this invention on forged alloys such as those having copper, zinc, magnesium, manganese or silicon as the principal alloying element with aluminum.

For purposes of clarification, in inverse wire drawing by shock, as to form a hollow cylindrical member, the element referred to as a matrix corresponds to a mold having a deep cavity of cylindrical shape and being open at one end thereof to receive the punch. The element referred to as the punch corresponds to a ram dimensioned to have a length corresponding to the depth of the cavity and a cross-section less than the cross-section of the cavity to provide an annular space in between when the punch is displaced lengthwise into the cavity. The bloom corresponds to a deformable metal of disc shape having a diameter corresponding somewhat to the diameter of the cavity and adapted to be inserted into the cavity. As the punch is displaced into the cavity, it presses the metal disc against the base of the cavity to cause the metal to flow outwardly and upwardly to fill the annular space. It is the surface of the bloom facing the punch that is. essentially zinc coated in accordance with the practice of this invention although others of the surfaces of the bloom may also be zinc coated if desired.

It will be understood that changes may be made in the details of application and operation without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. In a method for impact extrusion of an aluminum alloy billet having at least one surface for contacting a punch wherein said billet is confined in an open-ended cylindrical mold defining an extrusion cavity having an imperforate base and a peripheral wall, and a punch, having a length corresponding to the depth of said cavity and a cross section less than the cross section of said cavity to provide an annular space between said punch and said peripheral wall, is displaced into the open end toward said base of said cavity to cause a portion of said billet to flow into said annular space in a direction opposite to the direction of displacement of said punch, the improvement comprising providing said at least one surface with a coating of zinc prior to displacement of said punch into said cavity whereby adherence of particles of said aluminum alloy billet to the extrusion punch is substantially avoided to provide a smooth extruded surface.

2. The process as claimed in claim 1 in which the zinc coating is applied on the surface of the aluminum alloy by chemical means.

3. The process as claimed in claim 1 in which the zinc coating is applied on the surface of the aluminum alloy by electroplating.

4. The process as claimed in claim 1 in which the zinc coating as applied on the surface of the aluminum alloy by sputtering.

5. The process as claimed in claim 1 in which the zinc coating is applied on the surface of the aluminum alloy by means of application of molten zinc.

6. The process as claimed in claim 1 in which the aluminum alloy has for its principal alloying elements one or more of the metals selected from the group consisting of copper, zinc, magnesium, manganese and silicon.

References Cited UNITED STATES PATENTS 2,288,762 7/1942 Winkler 7247 3,152,059 10/1964 Wellington 72258 2,987,814 6/1961 Singleton et al. 29l97 3,046,640 7/1962 Singleton 29l97 3,177,579 4/1965 Singleton 29l97 3,268,358 8/1966 Bothwell 117-131 3,390,970 7/1968 Bothwell 29-197 CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner US. Cl. X.R. 72258, 267 

